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April 24, 1956 Filed Nov. 6, 1944 April 24, 1956 F. FII-:SER ETAL BURSTER 2 Sheets-Sheet 2 Filed NOV. 6, 1944 United States Patent O BURSTER Louis F. Fieser, Belmont, and Emanuel B. Hershberg, Stoughton, Mass., assignors to the United States ot y America as represented by the Secretary of War Application November 6, 1944, Serial No. 562,220

1 Claim. (Cl. 102-6) The invention described herein may be manufactured and used by or for the Government, for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to la burster for scatter type chemical bombs and particularly for incendiary oil bombs.

The known incendiary bombs can be classified as belonging to one or the other of two broad types. `One type, called the intensive type, is exemplified by the 2 to 4-lb. solid magnesium and thermite bombs, and is designed to remain substantially intact after the firing of the fuze and to burn progressively as a unit. The second type embodies a metal casing, usually made of steel, which serves primarily as a container for an incendiary filling of combustible material such as gelled gasoline, cotton waste or other fibrous material saturated withv a hydrocarbon fuel, or a pyrotechnic paste or gel incorporating a light metal, an organic fuel, and an oxygencontaining compound; the characteristic feature of the bombs of the second type is that on functioning of the fuse the incendiary filling is ejected from the casing and distributed over a certain area of the target in the form of a number of burning masses. The distribution and ignition of the incendiary charge has been effected either by ejection from the tail of the intact bomb or by burster principle, wherein an explosive charge contained in a burster tube, or central tube extending down the center of the bomb, ruptures the metal casing and hurls masses of the ignited filling in all directions.

A primary object of the present invention is to provide improvement of the known devices for igniting and distributing the charge of burster-type incendiary bombs. One widely used burster is a central tube charged with `black powder, but this has definite disadvantages and limitations. The distribution of the incendiary charge varies widely from bomb to bomb and is often very irregular; the charge is sometimes thrown in one direction only, and is sometimes all forced out of either the nose or tail of the bomb. The relatively slow-acting black powder builds up pressure in the container until a bursting point is reached, and the container then gives way at some one point of least resistance, which may vary from unit to unit. The percentage ignition is poor, and a considerable portion of the incendiary charge usually is. lost in the form of a flash burn: an explosive combustion of incendiary material which is vaporized or fragmented by the powder burster. The percentage ignition is improved somewhat by the incorporation of a certain amount of magnesium or other metal into the black-powder burster charge, but this variation does not correct the faulty distribution or the irregularity of operation Aof the black powder burster.

The new preferred method of firing burster-type incendiary bombs consists in the use of a central steel burster tube charged with a high explosive surrounded by a'steel burster casing or body containing a material Or'composition capable of igniting the incendiary filling 2,742,856 Patented Apr. 24, 1956 of the bomb. A high explosive of the type exemplified by TNT (trinitrotoluene), tetryl, PETN (pentaerythritetranitrate), or cyclonite acts entirely differently from black powder, or other relatively slow operating explosives. The steel tubes of the burster unit assembly, also,-

the burster well are shredded into ribbons over their entire length, and the casing of the bomb is opened evenly from nose to tail, for the bursting force of the high explosive is exerted sideways 'and at such a high velocity that a clean side burst results even if there is a weak point at the nose or tail.y The igniting composition is thus driven evenly into all parts of the incendiary filling,

which is distributed uniformly over a wide area in a fullyv ignited form. A distinct advantage is that the detonation wave apparently opens the casing so rapidly that an excessive pressure is not developed and the explosion has relatively little damaging effect upon the filling, for ex-.

of the group exemplified by diethylzinc, triethylboronf sodium-potassium alloy, phosphorus in phosphorus sesquisulfide. In short any material or composition that is either spontaneously inflammable or capable of reaching its kindling temperature under the action of a high explosive is capable of functioning as an igniter. White phosphorus is one of the simplest, and is a generally satisfactory igniting agent. lt is highly fragmented by the detonation of the high explosive 'and the fragments ignite readily and burn progressively as they are hurled through the air. The resulting ignition of the main incendiary charge is excellent, even when the bomb is fired after exposure to low temperatures encountered in highaltitude bombing operations (-40" El).

Since phosphorus itself is an incendiary substance,

albeit of rather low effectiveness, this igniter increases the total incendiary load carried. Of much more signifi-f cance is the fact that the phosphorus gives rise to a denseA smoke which has a screening and irritating effect con- 4situting a distinct deterrent to the fire-fighter. A further advantage is that pieces of phosphorus imbedded in ejected masses of a gasoline `gell frequently lead to reignition after the initial fire has been put out. Bombing tests on house structures have shown that reignition of the charge, with consequent firing of the target, occurs p after irregular periods as long as 10-12 hours. For these reasons, white phosphorus is a preferred igniter, just as TNT, with a booster charge of tetryl, is a preferred burster element because of its insensitivity to premature detonation on impact of a bullet.

but other combinations, as mentioned above, also fall within the scope of the invention. Furthermore, thereis no known limitation with respect to the incendiary filling; all fillings capable of being distributed and ignited by a black powder burster, with or without the incorporation of a light metal, can be distributed and ignited with the present burster, usually with markedly improved results.

In general design, a burster unit constructed in accordance with the present invention for insertion into a burster Well of a standardized chemical bomb may be characterized as comprising an outer metallic tube closed at its ;sealed at its other end where it is engaged with an inner The combination of these two preferred elements is illustrated in the examples,

3 corceintricmetallic tuberwhich serves as a container for an explosiverburster charge, said innertube beingy opened at its end engaged to the outertube, closed at its opposite end, and being spaced from the outer tube, so that the cniiiied'space in between lcan bel charged with'a suitable amountiof anigniting composition'. The'formation and position of: the two' metallicv tubes are such as to facilitateillingand'assembling, to provide satisfactory functioning inzcooperation with a fuse placed adjacent the open end ofthein'nerl tube, and to make a-leakproof container for the igniting composition. The explosive burster charge isfadva'ntageously loaded as a unit in a container relatively thinner orweakerl than the inner metallic tube into whichit is inserted. To aid in having each of the componentsrin the burster unit'properly positioned, anI aligning? structure isdisposed at the closed tail end of the outer tube and a-coiled 'spring may be placed in theinner tube tolbe'compressed between the closed end of the inner tube and the explosive burster container. A more detailed description of these components and other features'ofthe'invention will be given with reference'to the accompanying drawings which illustrate a practical embodiment of thev improved burster unit adapted for a 1D0-lb. oil lled bomb.

*In the drawing:

Figure- 1` illustrate an elevational side view of va stand,- ardized G-lb. chemical bomb, known as the M47, with parts lcut away to show the' positioning of the fuse and burster;

Figure 2'shows a cross-sectional view along the longitudinal axis of the burster unit on a relatively enlarged scale'with reference to Fig. l and with an intermediate portion broken away;

Fig. y3 yshows in elevation a front end view of the burster unit` where a nose fuse is seated;

Fig'. 4 is a cross-sectional view of the inner metallic tube component of the burster unit taken along itslongitudinalaxis;

Fig. 5 is a longitudinal cross-sectional view of the explosive burster container which fits into the inner metallic tube and is on an enlarged scale with reference to Figs.A 3 and. 4.

Referring to Fig. 1, the bomb has a cylindrical body 6, aspherical nose 7, and a box tail tin assembly 8. The cylindrical portion is about 8 inches in diameter and the overall length is approximately 48 inches. The body may be made of rolled and lap-welded sheet steel, 3/32 inch thick. When empty, the bomb weighs about pounds, and when filled with an incendiary oil, it weighs about 85 pounds. Y An adapter 9 atV the nose end connects:

relationship to the positioning ofthe burster unit, sinceA the burster unit with which this invention is concerned maybe utilized with various types of fuses andbombs.

lIn general, chemical scatter type bombs requiring ,the useof burster may be lled with chemical agents whichproduce a toxic or irritating physiological effect, a screeningsmoke, an incendiary action, or a combination of these'elects. Chemical bombs are most effective when they function above ground; therefore they are fitted -with nose fuses which give super-quick action or time fuses for giving an air burst. Generally, the burster is desired to rupture the bomb body for'releasing the ller sothat the released filler spreads out over the ,ground without being too widely diffused, and this is particularly true of incendiary bombs, smoke bombs, non-persistent agent bombs, and to some extent, of persistent agent bombs.

Chemical bombs are designed for single suspension in either horizontal or vertical bomb racks. The suspension lugs 13 on the side of the bomb are for horizontal suspension by shackles. When ready for release, the bombardier manipulates a control which immediately frees the bomb from the shackles. The arming wire 14, securely attached to the aircraft, snaps taut and pulls free of the nose fuse 12 allowing the arming vane 15l to-be` rotated by the air stream when the. released bomb is falling. After a number of rotations of the arming vane 15 the safety pin becomes removedso that. thefuse becomes armed, and upon impact, a tiring pin is driven into a primer, which in turnl initiates detonation of the burster explosive. The detonation of the explosive should be instantaneous for effective scattering of the chemical filler.

For convenience and safety in shipment or handling, it is generallydesirable to be able to` ship the bomb `bodies unfused, uniilled, and without the burster inserted in the, burster well; therefore, it is important that the burster components be designed-to simplify the filling and assembling of the `complete bomb in'the field. For lling, the burster well 10 is Vunscrewed and removed, and the ller is put into the empty bomb, nose up, until the level of Athe filler is about 6 inches below the mouth of the fillinghole, so that the burster well can be reinserted with allowance of suitable outage.

Referring to Figures 2, 3, 4 and 5, the outer tube 16 of the burster unit whichis to be inserted into the burster well 10, is of suitable diameter to have a closed fit in the well 10' -and of suicient length to extend approximatelyy to the end of the well 10. The outer tube 16 may be made from hot rolled steel, pickled, or cold rolled steel with a soft skin-rolled temper and` dull finish. The tube` diameter is 1% inches, the wall thickness is about 0.0598 inch (No. 16 Std. gage) the end closure disc 17 may be attached by a spot-welding followed by brazing and welding around the entire periphery. Into the front (nose end) of the tube of the outer tube 16 is mortised a collar 18 having an internally threaded center hole 19. This collar may besealed tightly by silver brazing to the inner wall of outer tube 16 atthe periphery 20 of the narrow neck portion extending into tube.16. The thread 19 engages the thread. 21 on the plug 22, which is secured to the open end of the inner metal tube 23. The plug 22 may be secured? to the tube 23 by silver brazing at the juncture 24. Theopposite end of the metallic tube 23 may be closed by a cup shaped disc 25 also 'ixedby silver brazing. When this inner tube 23 is inserted into the outer tube 16 with its plugattachment 22 screwed tightly into, the collar 18, the. closedl end 25 extends to about l to 2 inchesfrom the closed end 17 of the; outer tube 16. The` threadingd19 and 21` onY the collar and plug maybe tapered, and; it is preferred' that a gasket 26, be` inserted between-.a shoulderont the collar 18 and acorresponding` shoulder on the plug 22.

A socket arrangement of` two, generally U-shaped,

strips of metal 27, about No. 16 Std. gage, and spot-'- welded tothe adjacent endl closure 17 of the outer tube 16: where, theyy cross, serves.y as an aligner for keepingy the innerwtube 23A centrally spaced throughoutl its lengthinside the outer tube 16.

A preferred form of the unit explosiveburster container which isA to beinserted into the open'V end of `theinner mbev 23 is shown in,y Fig. 5, This container comprises a tube 28 made ofiflaminated paper impregnated'with a suitablercsin to increase itsV strength and impart moisture-resistant qualities, with two soft metal caps 29 to close both 'ends'. The caps 29'may be sealed tightly to the ends of the tube 28 wi'thfa suitable cement, suchV as a thermo-setting resin cement 'of the alkyd type. A suitable charge to form the core o'f'containe'r'ZS is madev b'y placing two pellets Btl-of tetryl at both ends of the tube 28 and intermediate these pellets a main charge 31 of TNT.

The explosive burster container may be varied in character. The shell 28 of the container may be made of any relatively light material which is readily ruptured, as for example, thin walled aluminum tubing or brass, or the outer covering of the explosive charge may be simply a waterproof textile such as encloses PETN (pentaerythritetranitrate) in detonating cord, known commercially as Primacord. The symmetrical arrangement of the burster and main burster explosive inside the container 28 is benecial for preventing mistakes in loading the container into the inner tube 23 and also for insuring instantaneous explosion.

To further facilitate assembling of the burster unit, a coiled spring 32 is inserted into the inner tube 23 so that one end rests against the bottom closure 2S and the other end is pressed by the inner (rear) end 29 of the explosive burster container 28 when it is inserted into the inner metallic tube 23, the explosive container 28 being pushed into position so that its outer (front) end 29 is substantially ilush with the front (nose end) of the burster unit where the gaine of fuse 12 seats contiguously when the burster unit and the fuse are assembled with the burster well in the bomb.

The space 33 between the inner tube 23 and outer tube 16 and surrounding the aligner members 27 may be considered to be the igniting substance well for lling with the materials such as WP or others mentioned. The assembled burster unit including the closed outer tube 16 and the inner tube 23 with its one end closed, should have adequate pressure resistance for safe use; they should be fabricated, in general, to avoid rupture, distortion, or leakage when subjected to an internal air pressure of 200 pounds per square inch.

In assembling the burster unit for shipment, rst the outer tube 16, having closed end 17 and the collar 18 attached but with inner tube 23 removed, is partially filled as a container for the igniting substance, such as WP, leaving enough room so that the inner tube 23 can be inserted and screwed in tightly. This container may be filled approximately one-half full with hot water at about l20l30 F. The water is preferably buifered with sodium-hydrophosphate, sodium carbonate, or any other suitable alkaline salt to maintain a pH value between about 6.5 and 8.0. The WP is melted and maintained at a temperature no higher than about 55 C.' and no less than about 50 C. during the tilling operation. The partially lled container should allow room for inserting the inner tube 23 for closing. It is desirable that the depth of residual water on the WP in the container not exceed 0.25 inch.

The thus 'illed WP container is closed by placing a lead gasket 26 on the shoulder in the container collar 18, inserting the inner tube 23, and screwing the plug 22 tightly into the collar 18 so as to compress the lead gasket 26 and tightly seal ot the threaded juncture between the plug 22 and the collar 18, the threads 21 on the plug 22 first being advantageously luted with basic carbonate white lead paste-in-oil, or equivalent luting material. 'Ihe thus iilled and sealed WP container portion of the burster unit may be shipped separately from the loaded burster explosive container 28, which is to be inserted into the inner tube 23 when the entire burster unit is to be placed in the burster well of a bomb at an airdrorne or complete bomb assembly point.

'Ihe burster unit is kept properly positioned in the burster well by having the bevelled flange 34 on the plug 22 seat in the fuse socket 35 of the burster well 10 so that the front end of the burster unit is close to the nose fuse 12. For some forms of fuses, the front opening 36 of the inner tube 23 may be chamfered also to provide a fuse seat. It is to be noted that it is desirable to have the explosive charge as close as possible to the fuse when the fuse functions.

y EXAMPLE In a suitable combination of parts, as illustrated in Figs. l to 5, the outer tube 16 is filled with enough WP (White phosphorus) to provide a 5% outage and the inner tube 23 is screwed into the outer tube 16 while the charge is still molten; the unit subsequently is screwed into the bomb after this has been loaded, for example with gasoline gelled with an aluminum soap, with an isobutyl methacrylate composition, or other thickener. The high explosive charge is loaded into the burster container 28, conveniently in the form of pellets, and the bomb is armed by inserting this explosive container 28 into the inner tube 23 and attaching the nose fuse 12. In this design, closure of the phosphorus well between outer tube 16 and inner tube 23, is eiected by means of a tapered thread 19. A preferred method of closure employs a lead gasket 26.

The burster tube is preferably made of laminated paper- Bakelite (phenol-formaldehyde resin). Fibre tube can be used, but variation in length with ageing, or under changing conditions of humidity, renders this material less certain of satisfactory performance. A suitable explosive charge is obtained with a 36 inch tube W16 inch O. D. and 2%.; inch I. D. iilled with 1A inch pellets molded at a compression of approximately 5,000 pounds sq. inch (density, 1.5 2-1.5 5 in a 5/16 inch die; TNT is pelleted in flake form, and tetryl is mixed with 2% graphite for pelleting. The main charge 31 is TNT, and two or three pellets 30 of tetryl are introduced at each end to act as a booster. The pellets are thrust in lightly with a wooden rod and the last one is left extending about 1A inch. The end of the tube is painted with Glyptal cement and the metal cap is put in place and forced on flush with the en'd of the tube, thus compressing slightly the column of pellets. The total charge is approximately 70 g.

The phosphorus chamber can be iilled by displacement of water at 5 5 C., but a simpler and more ecient method which provides complete insurance against corrosion by the action of phosphorized water consists in dry loading. Phosphorus is melted under water, drawn ot from the lower layer and run into a well that has been flushed with an inert gas; the charge is metered conveniently by measurement of the fall in the water level.

The phosphorus charge does not constitute a signicant source of hazard in the shipping or handling of an oil-filled bomb, or in carrying it on a bombing mission. Experiment has shown that a direct hit on the central burster tube by a 50-calibre armor-piercing machine gun shell from a range of 50 yards may rupture the burster and lay open a Va inch section of white phosphorus without producing a tire. Apparently the incendiary oil charge forms a thin iilm providing protection against air.

In a typical static test with a bomb loaded with 42 lbs. of Napalm gasoline gel the gum was distributed evenly in large globs over an area 64 x 81 yards, ignition was approximately 98%, and the fire count was as follows:

175-200 initial fires fires burned 3 minutes 60 tires burned 5 minutes 50 tires burned 8 minutes 25 tires burned 10 minutes 17 res burned l2 minutes In further tests, bombs were tired statically over a water pond. Those few globs that were not extinguished by dropping onto water were extinguished by operators within l minute. Of a total of 4210 pounds of soap gelled gasoline tired, 40 lbs. 2 oz. was recovered (95.6% which indicates that there is no appreciable loss due t0 a ash burn. The results were substantially the same when the bomb was lled with gasoline gelled with isobutylmethacrylate.

7 EXAMPLE 2.

tion-99%, distribution area,y 27 x:3:7;yds.). A gelrlled 500,-lb. bomb. with La. cast-ironr casing can 'be tiredl vsatisfactorily'with-ga2burster=containingr7tlbs; vof WP and va i, inch, `I. D. `tube containing; 228fijg. of --a= eutectic mix ture of TNT and tetryl. If :the casingof the lSOO-lb. bomb is-.made of steel, a? l-inch 4tube-:of:-theysamefmaterial. provides;.adequatec openingy andi. distribution.

The "100-lb.-bombchargdfwith'ta gel of8,% crepe rubber in gasoline,fcan,be,red satisfactorily with -a two strand,.Brimacordburster surrounded-by. 230,fg.,ofla mixture. of black .p ovvder;=` (lfpart), andfvmagnesiumfpowder (lpart). 'lhefchargeisdistributed4 in,1/21b.vglobs over an arealhaving a maximum radius of 411yds., and igni tion isat least 90%,

`Many testshavebeen made. with bombs, charged ywith a 'variety of:gell'edgaso1ines andotherincendiary illed and equipped with bursters designed in accordance with the'present'inven'tion; that the bursters were entirely satisfactoryfori'standardization. ",Fl'i'ese'burstersI permitl safe 'andeasyfshipmentof spontaneously ignitable substances-suchasWP, are easily assemb1ed-to-chemical bombs in the `field and functionv satisfactorily'in rupturing the bomb 'casin'gs other types of# chemicalfbombs. For example,y they/may beused=with or lwithout thevv WP or= igniting=substance for burstingl smoke bombs, e. g'., 'l bombs y*chargedf with ani FSf mixture f (sulfur ftriox-idef and chlorosulfonic acid) or FM (titanium .tetrachloride), or bombs loadedv withv toxic agents.

late a i nonfinjurious smoke bomb` orv to/ mark the hit:4 of thesbombron bursting.

Itzis' to abe understood that. although 1 theL inventionhas been. describedl in detail with reference '.to specicxmbodiments, otherfmodications,come Withintherspiritsand scope' thereof.

Weclaim.:

-I-n-a` burster-type oil incendiary bom-b,afbursterunit' comprising-` an. elongated-outer steelt tube dimensioned to.

fit contiguously into a tubular burster Well, a. relatively shorter inner steeltubezconcentrically-` spaced withinf-said outer steel tube, closurestattrear ends of-said,tubes, a threadedy attachmentbetween front -ends of the. said outer and inner tubes,atubular.containenloaded:with a central lcore of TNT compressed between rpelletstof tetryl disposed;- in the. inner tube,` and acoiledspring in the/inner tube betweenitsiclosed ,rear end..and-the tubular. container, pressing against saidtubular container-'so that: its front end is, pushed ush vviththey frontend oft-he inner steel tube.

References Cited` in the le' ofthis.. patent UNITED STATES PATENTS 1,294,150 ortiz Feb. 11, 19.19 1,311,521 Johnson July 29, 1919 1,333,786 VTimms Mar. 16, 1920 1,484,190 Ray Feb. 19, 1924 1,791,716v 'Davis et al. ,Feb. 10, 193 1 1,878,491 'Goss sept. 20, 1932 FOREIGN PATENTS *525,972* .Great Britain sept. 9, 1940 The "results of" these tests proved' Although theburstersarefparticularly useful in'incendiary'bombs they`v may be Y used 'Iwithobvious modifications inl various' In the latter use WP or some similar agenmnay f be desired: infthe bursterfunitt for makingi the bombx simu- 

